The present invention relates generally semiconductor fabrication and, in particular, to a system and methodology for forming a conductivity facilitating layer via chemical vapor deposition (CVD) utilizing a metal organic (MO) precursor.
In the semiconductor industry there is a continuing trend toward increasing device densities, throughput and yield. To increase device densities there have been, and continue to be, efforts toward scaling down semiconductor device dimensions (e.g., at sub-micron levels). In order to accomplish such densities, smaller feature sizes and more precise feature shapes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry, such as corners and edges, of various features. To increase throughput, the number of required processing steps can be reduced and/or the time required for those processing steps can be reduced. To increase yield, which is the percentage of finished products that leave a fabrication process as compared to the number of products that enter the fabrication process, control and/or quality of individual fabrication processes can be improved.
Semiconductor fabrication is a manufacturing process employed to create semiconductor devices in and on a wafer surface. Polished, blank wafers come into semiconductor fabrication, and exit with the surface covered with large numbers of semiconductor devices. Semiconductor fabrication includes a large number of steps and/or processes that control and build the devicesxe2x80x94basic processes utilized include layering, doping, heat treatments and patterning. Layering is an operation that adds thin layers to the wafer surface. Layers can be, for example, insulators, semiconductors and/or conductors and are grown or deposited via a variety of processes. Common deposition techniques include, for example, evaporation and sputtering. Doping is a process that adds specific amounts of dopants to the wafer surface. The dopants can cause the properties of layers to be modified (e.g., change a semiconductor to a conductor). A number of techniques, such as thermal diffusion and ion implantation can be employed for doping. Heat treatments are another basic operation in which a wafer is heated and cooled to achieve specific results. Typically, in heat treatment operations, no additional material is added or removed from the wafer, although contaminates and vapors may evaporate from the wafer. One common heat treatment is annealing, which repairs damage to crystal structure of a wafer/device generally caused by doping operations. Other heat treatments, such as alloying and driving of solvents, are also employed in semiconductor fabrication.
The volume, use and complexity of computers and electronic devices are continually increasing as computers are consistently becoming more powerful and new and improved electronic devices are continually developed (e.g., digital audio players, video players). Additionally, the growth and use of digital media (e.g., digital audio, video, images, and the like) have further pushed development of these devices. Such growth and development has vastly increased the amount of information desired/required to be stored and maintained for computer and electronic devices.
Generally, information is stored and maintained in one or more of a number of types of storage devices. Storage devices include long term storage mediums such as, for example, hard disk drives, compact disk drives and corresponding media, digital video disk (DVD) drives, and the like. The long term storage mediums typically store larger amounts of information at a lower cost, but are slower than other types of storage devices. Storage devices also include memory cells which are often, but not always, short term storage mediums. Short term memory cells tend to be substantially faster than long term storage mediums. Such short term memory cells include, for example, dynamic random access memory (DRAM), static random access memory (SRAM), double data rate memory (DDR), fast page mode dynamic random access memory (FPMDRAM), extended data-out dynamic random access memory (EDODRAM), synchronous dynamic random access memory (SDRAM), VideoRAM (VRAM), flash memory, read only memory (ROM), and the like.
Memory cells can generally be subdivided into volatile and non-volatile types. Volatile memory cells usually lose their information if they lose power and typically require periodic refresh cycles to maintain their information. Volatile memory cells include, for example, random access memory (RAM), DRAM, SRAM and the like. Non-volatile memory cells maintain their information whether or not power is maintained to the devices. Non-volatile memory cells include, but are not limited to, ROM, programmable read only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), flash EEPROM the like. Volatile memory cells generally provide faster operation at a lower cost as compared to non-volatile memory cells.
Memory cells often include arrays of memory cells. Each memory cell can be accessed or xe2x80x9creadxe2x80x9d, xe2x80x9cwrittenxe2x80x9d, and xe2x80x9cerasedxe2x80x9d with information. The memory cells maintain information in an xe2x80x9coffxe2x80x9d or an xe2x80x9conxe2x80x9d state, also referred to as xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d. Typically, a memory cell is addressed to retrieve a specified number of byte(s) (e.g., 8 memory cells per byte). For volatile memory cells, the memory cells must be periodically xe2x80x9crefreshedxe2x80x9d in order to maintain their state. Such memory cells are usually fabricated from semiconductor devices that perform these various functions and are capable of switching and maintaining the two states. The devices are often fabricated with inorganic solid state technology, such as, crystalline silicon devices. A common semiconductor device employed in memory cells is the metal oxide semiconductor field effect transistor (MOSFET).
The proliferation and increased usage of portable computer and electronic devices has greatly increased demand for memory cells. Digital cameras, digital audio players, personal digital assistants, and the like generally seek to employ large capacity memory cells (e.g., flash memory, smart media, compact flash, . . . ). The increased demand for information storage is commensurate with memory cells having an ever increasing storage capacity (e.g., increase storage per die or chip). A postage-stamp-sized piece of silicon may, for example, contain tens of millions of transistors, each transistor as small as a few hundred nanometers. However, silicon-based devices are approaching their fundamental physical size limits. Inorganic solid state devices are generally encumbered with a complex architecture which leads to high cost and a loss of data storage density. The volatile semiconductor memories based on inorganic semiconductor material require a near constant supply of electric current, which produces heating and high electric power consumption in order to merely maintain stored information. Non-volatile semiconductor memory cells, which are also based on inorganic semiconductor material, do not require such constant supplies of power in order to maintain stored information. However, non-volatile semiconductor memory cells have a reduced data rate, high power consumption and a large degree of complexity as compared with typical volatile memory cells.
Further, as the size of inorganic solid state devices decreases and integration increases, sensitivity to alignment tolerances can also increase making fabrication markedly more difficult. Formation of features at small minimum sizes does not imply that the minimum size can be used for fabrication of working circuits. It is necessary to have alignment tolerances which are much smaller than the minimum size, such as one quarter the minimum size, for example. Thus, further device shrinking and density increasing may be limited for inorganic memory cells. Furthermore, such shrinkage for inorganic non-volatile memory cells, while meeting increased performance demands, is particularly difficult to do while maintaining low costs.
A promising, relatively recent type of memory cell is an organic based memory cell. Organic memory cells are at least partly based on organic materials and, are thus able to overcome some of the limitations of inorganic based memory cells. Organic memory cells facilitate increases in device density while also increasing device performance relative to conventional inorganic memory cell. Additionally, organic memory cells are non-volatile and, as such, do not require frequent refresh cycles or constant power. The cells of the organic memory cell can have two or more states corresponding to various levels of impedance. These states are set by applying a bias voltage and then the cells remain in their respective states until another voltage, in reverse bias, is applied. The cells maintain their states with or without power (e.g., non-volatile) and can be read either electrically or optically by measuring injection current or light emission, for example.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its purpose is merely to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
According to one or more aspects of the present invention, a system and methodology for forming a passive layer on a conductive layer, such as can be done during fabrication of an organic memory cell, are disclosed. The passive layer generally includes a conductivity facilitating compound, such as copper sulfide (Cu2S), and is deposited onto the conductive layer via plasma enhanced chemical vapor deposition (PECVD) utilizing a metal organic (MO) precursor. The precursor facilitates depositing the conductivity facilitating compound in the absence of toxic hydrogen sulfide (H2S), and at a relatively low temperature and pressure (e.g., between about 473 to 573 K and 0.2 Pa., respectively). The deposition process can be monitored and controlled to facilitate, among other things, depositing the conductivity facilitating compound to a desired thickness.
To the accomplishment of the foregoing and related ends, certain illustrative aspects of the invention are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.